The major contributor to liver diseases, cirrhosis and hepatic carcinoma, is infection of hepatitis type C virus (HCV). Mouse liver, engrafted with human hepatocytes, can be used to study HCV infection and develop related vaccines. The objective of this application is to create a Rag-2-/- gammac-/- Fah-/- triple-knockout mouse, which will have enhanced capacity of human hepatocyte engraftment compared with previous models. Fah-/- mice allow robust liver repopulation while Rag-2-/- gammac-/- mice are significantly more immune deficient, allowing better human hematopoietic reconstitution than NOD/SCID or SCID mice. To generate the Rag-2-/- gammac-/- Fah-/- triple-knockout mice, we will crossbreed Fah-/- and Rag-2-/- gammac-/- mice. Human hematopoietic stem cells and mouse hepatocytes will be transplanted separately into the Rag-2-/- gammac-/- Fah-/- mice to verify the combined features of liver repopulation capacity and immune deficiency. Then, human hepatocyte engraftment in the triple knockout mouse will be assessed by single or serial human hepatocyte transplantation. Subsequently, therapeutic correction of liver disease will be, for the first time, used as a functional marker to determine human hepatocyte engraftment. Rag-2-/- gammac-/- Fah-/- triple-knockout mouse, displaying enhanced human hepatocyte engraftment, will have an important positive impact on HCV related research. In addition, the Rag-2-/- gammac-/- Fah-/- triple-knockout mice will provide a model system for study of human liver biology as well as a transplantation model for study of human oval and ES derived liver-like cells.